The present invention deals with a method and equipment for introducing pitch and roll attitude information in a piloting instrument such as a gyro horizon type of instrument.
A fundamental indication for the piloting of aircraft, particularly in low external visibility conditions, is attitude which is displayed to the pilot by an instrument called the artificial horizon. The aircraft position in pitch and roll is normally displayed in this instrument by a fixed symbol representing the aircraft wings, behind which a line remains parallel to the horizon and vertical to indicate displacement in roll and pitch movements, respectively. To facilitate piloting at large pitch angles there are in most of the cases, on either side of the main line depicting the horizon, other lines parallel to the main one that can be graduated in pitch angles. Most of the time, for practical use, a manual adjustment permits the displacement of the aircraft symbol either up or down.
Artificial horizons in the beginning were self-contained instruments including a gyroscope slaved to the vertical by a gravity sensing monitoring system called the erector. However, these reliable and very useful instruments are subject to errors inherent in the principle of gyroscopes.
The advent of more sophisticated gyroscopic references, particularly the so-called inertial references, made it possible to obtain an indication of the vertical with a much higher accuracy on board an aircraft. This led to the use of artificial horizons with a conventional display but actuated by servomechanisms reproducing pitch and roll electrical signals furnished by appropriate transducers in the gyroscopic reference. Most of the time these remote indicators also provide other indications for the control of the aircraft and they become sophisticated indicators generally known as "flight directors." These instruments usually have rather large dimensions which permit an increase in the sensitivity of the indications and improve the readability. They are located in a privileged position in front of the pilot, in the middle of the instrument panel. As a counterpart and due to the complexity of the gyroscopic reference, indicator servomechanisms, and electrical connections between the two parts of the equipment, the risks of failure are much higher than with a self-contained artificial horizon.
Also when it happens that an electrical power failure occurs for any of various reasons (a lightning strike for example) this can immediately make the vertical reference system unserviceable.
The above reasons lead to the completion of the aircraft installation with a highly reliable case contained emergency gyroscopic horizon of a moderate price, the most elaborate versions of which display reliable information several minutes after power cut-off, the gyro coasting down. It has been proven in several instances that such an indicator can help in the recovery of an aircraft in difficulty.
As space is usually very limited on instrument panels, an emergency horizon has reduced size and is located somewhat aside. For these two reasons its use, when it becomes necessary, is not always very practical.